1. Technical Field
The present invention relates to a wavelength tunable interference filter, a method for manufacturing the wavelength tunable interference filter, an optical module, and an electronic apparatus.
2. Related Art
There is a known wavelength tunable interference filter in which reflection films are disposed on the opposing surfaces of a pair of substrates so that the reflection films face each other and the dimension of the gap between the reflection films is changed to selectively extract light of a predetermined wavelength from incident light and transmit the extracted light.
In a wavelength tunable interference filter of this type, when the reflection films are made, for example, of Ag or an Ag alloy, the reflection films are likely to deteriorate due to adhesion of foreign matter, such as the air and water molecules in the air, on the reflection films.
In contrast, there is a wavelength tunable interference filter in which a space where the reflection films and electrodes are provided is hermetically sealed and the sealed space is exhausted into a vacuum (see JP-T-10-511772, for example).
In the filter detector described in JP-T-10-511772, one of a pair of substrates on which reflection films are formed is bonded to another substrate with the other one of the pair of substrates interposed therebetween, whereby a space in which the reflection films and electrodes that form an actuator are provided is exhausted into a vacuum and hermetically sealed.
In JP-T-10-511772 described above, in which each of the substrates is formed of a silicon substrate, a voltage is able to be applied to the electrodes via the silicon substrates. A silicon substrate, however, does not transmit light, for example, in the visible region. In a wavelength tunable interference filter that transmits light, for example, in the visible region, each substrate is made of glass or any other suitable nonconductive material, and the configuration described in JP-T-10-511772 undesirably does not allow application of a voltage to the electrodes in a hermetically sealed space.